Question

Name the three stages of the cell respiration of glucose and state where in the cell each takes place and whether or not oxygen is required. (p. 403 )

Short answer

Answer: The three stages of cellular respiration of glucose are 1) Glycolysis, 2) Krebs Cycle (Citric Acid cycle or TCA cycle), and 3) Oxidative Phosphorylation (Electron Transport Chain). Glycolysis takes place in the cytoplasm and does not require oxygen. The Krebs Cycle occurs in the mitochondrial matrix and does not directly use oxygen but requires its presence for the Electron Transport Chain to function efficiently. Oxidative Phosphorylation occurs in the inner mitochondrial membrane and requires oxygen as the final electron acceptor.

Step-by-step solution

Identify the three stages of cellular respiration of glucose

The three stages are: 1) Glycolysis, 2) Krebs Cycle (Citric Acid cyle or TCA cycle), and 3) Oxidative Phosphorylation (Electron Transport Chain).

Locate where each stage takes place within the cell

1) Glycolysis takes place in the cytoplasm; 2) Krebs Cycle takes place in the mitochondrial matrix; 3) Oxidative Phosphorylation takes place in the inner mitochondrial membrane.

Identify if oxygen is required at each stage

1) Glycolysis does not require oxygen and can proceed anaerobically (with or without O2). 2) Krebs Cycle does not directly use oxygen, but it requires the presence of O2 for the efficient functioning of the Electron Transport Chain (ETC). 3) Oxidative Phosphorylation requires oxygen as it is the final electron acceptor in the ETC.

Key concepts

Glycolysis

Glycolysis is the first stage of cellular respiration and takes place in the cytoplasm of the cell. During this process, glucose, a six-carbon sugar, is broken down into two three-carbon molecules called pyruvate. This is achieved through a series of ten steps, each facilitated by specific enzymes.

Glycolysis can occur with or without oxygen, making it an anaerobic process. This means that cells can continue to produce ATP in low-oxygen environments. Although glycolysis generates only a small amount of ATP compared to the other stages, it provides quick energy through substrate-level phosphorylation.

It's important to note that glycolysis produces 2 ATP molecules and 2 NADH molecules, which are used in subsequent stages of cellular respiration.

Krebs Cycle

The Krebs Cycle, also known as the Citric Acid Cycle, is the second stage of cellular respiration. It takes place in the mitochondrial matrix, which is the innermost compartment of the mitochondrion. Glycolysis products lead into the Krebs Cycle when pyruvate is transformed into acetyl-CoA.

During the Krebs Cycle, acetyl-CoA combines with a four-carbon molecule to form citrate, initiating a series of reactions that release carbon dioxide. Even though it doesn’t directly require oxygen, the Krebs Cycle relies on the presence of oxygen because it allows for the efficient functioning of the electron transport chain, where most ATP is generated.

The cycle generates ATP through substrate-level phosphorylation and produces important electron carriers, NADH and FADH2, which facilitate ATP production in the next stage.

Oxidative Phosphorylation

Oxidative Phosphorylation is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. It consists of the Electron Transport Chain (ETC) and chemiosmosis. This stage is oxygen-dependent because oxygen serves as the final electron acceptor in the ETC.

In oxidative phosphorylation, electrons from NADH and FADH2 are transferred through a chain of proteins embedded in the inner mitochondrial membrane. This electron movement generates an electrochemical gradient, as protons (H+) are pumped across the membrane, creating potential energy.

Finally, ATP is synthesized as protons flow back through ATP synthase. This process is highly efficient, producing the majority of ATP in cellular respiration, approximately 34 ATP molecules from a single glucose molecule.

Mitochondria

Mitochondria are often referred to as the powerhouses of the cell due to their crucial role in energy production via cellular respiration. They possess a double membrane structure—an outer membrane and a folded inner membrane, known as the cristae, where oxidative phosphorylation occurs.

The space enclosed by the inner membrane is called the mitochondrial matrix, where the Krebs Cycle takes place. Mitochondria also contain their own DNA, allowing them to produce some of their own proteins essential for energy metabolism.

Mitochondria are crucial not only for producing ATP but also for other roles such as regulating cell metabolism, signaling, and apoptosis.

Cytoplasm

The cytoplasm is the jelly-like substance that fills the inside of a cell and surrounds the organelles. It is primarily composed of water, salts, and proteins, providing the medium for biochemical processes.

Glycolysis occurs in the cytoplasm, highlighting its role as a hub for essential enzymatic reactions required for initial energy extraction. Since glycolysis doesn't require organelles, it takes full advantage of the cytoplasmic environment.

Beyond supporting metabolism, the cytoplasm plays a role in maintaining cell shape, storing nutrients and waste products, and facilitating communication between different parts of the cell.